DOCS-15260 prevent dropping shard key index when alternative index doesn't exist (#1071)

* updates dropIndexes and db.collection.dropIndexes

* spacing;

* fix include path

* updates top-level desc

* typo

* internal review feedback

* external feedback

* external round 2

Author: jmd-mongo

source/includes/fact-drop-indexes-6.0.rst

@@ -0,0 +1,5 @@
+Starting in MongoDB 6.0, |drop-index| raises an error if you attempt
+to use it to remove the last remaining shard key compatible index. 
+Passing ``"*"`` to |drop-index| drops all indexes except 
+the ``_id`` index and the last remaining shard key compatible index, 
+if one exists.

source/reference/command/dropIndexes.txt

@@ -12,10 +12,12 @@ dropIndexes
 
 .. dbcommand:: dropIndexes
 
+   .. versionchanged:: 6.0
+   
    The :dbcommand:`dropIndexes` command drops one or more indexes
-   (except the index on the ``_id`` field) from the specified
-   collection.
-
+   (except the index on the ``_id`` field and the last remaining shard
+   key index, if one exists) from the specified collection.
+   
    The command has the following form:
 
    .. code-block:: javascript
@@ -42,15 +44,17 @@ dropIndexes
 
         - The index or indexes to drop.
 
-          - To drop all but the _id index from the collection,
-            specify ``"*"``.
+          - To drop all indexes except the ``_id`` index and the last 
+            remaining shard key index from the collection if one 
+            exists, specify ``"*"``.
 
           - To drop a single index, specify either the index name,
             the index specification document (unless the index is a
             :doc:`text </core/index-text>` index), or an array of the
             index name. To drop a :doc:`text </core/index-text>` index,
             specify the index names instead of the index specification
-            document.
+            document. If this index is the last remaining shard key 
+            index, ``dropIndexes`` raises an error.
 
           - To drop multiple indexes (Available starting in MongoDB
             4.2), specify an array of the index names.
@@ -75,6 +79,8 @@ Behavior
 
 .. |drop-index| replace:: :dbcommand:`dropIndexes`
 
+.. include:: /includes/fact-drop-indexes-6.0.rst
+
 .. include:: /includes/fact-drop-index-5.2.rst
 
 Kill related queries only

source/reference/method/db.collection.dropIndexes.txt

@@ -21,7 +21,8 @@ Definition
 
 
    Drops the specified index or indexes (except the index on the
-   ``_id`` field) from a collection.
+   ``_id`` field and the last remaining shard key index) from a 
+   collection.
 
    You can use the method to:
 
@@ -111,6 +112,8 @@ Behavior
 
 .. |drop-index| replace:: :method:`db.collection.dropIndexes()`
 
+.. include:: /includes/fact-drop-indexes-6.0.rst
+
 .. include:: /includes/fact-drop-index-5.2.rst
 
 Kill related queries only

source/release-notes/6.0-compatibility.txt

@@ -41,6 +41,15 @@ Change Streams
 Indexes
 -------
 
+Last Remaining Shard Key Index Cannot be Dropped Inadvertently
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting in MongoDB 6.0, passing ``"*"`` to :dbcommand:`dropIndexes` or
+:method:`db.collection.dropIndexes()` drops all indexes **except**
+for the ``_id`` index and the last remaining shard key index, if one 
+exists. Attempts to explicitly drop the last remaining shard key index 
+raise an error.
+
 Existing Indexes Can Be Dropped During an Index Build
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~